What does NEC4 clause 60.1(19) mean?

It is the hardest clause in the list to meet. It has four conditions, and each must be shown. First, the event stops you completing the whole of the works, or completing them by the date on the Accepted Programme. Stops means stops. An event that only makes the work slower or dearer does not count. Second, neither party could prevent it. That rules out anything within either side's control, including their suppliers. Third, an experienced contractor would have judged at the Contract Date that it was so unlikely that allowing for it was unreasonable. This is the same test as for physical conditions under clause 60.1(12), and a risk known at signing fails it. Fourth, it is not one of the other compensation events. Notify under clause 61.3 within 8 weeks of becoming aware it has happened. Give an early warning under clause 15.1 the moment it is foreseeable. Where an experienced contractor could have warned, clauses 61.5 and 63 require the event to be assessed as if a warning had been given. The change to the Prices, your contract price, is assessed under clause 63.1. It is the effect on actual Defined Cost up to the notification and forecast Defined Cost after it, plus the Fee. That generally means standing resources, protecting the works and remobilising. Two things go wrong most. You notify a general disruption, such as a supply shortage that made materials dearer, when nothing stopped completion. Or you cannot show the event was unforeseeable at the Contract Date. Any delay to the Completion Date is assessed separately under clause 63, and that is a job for your planner.